The proposed research program is a basic science (non-clinical) evaluation of a known ultrasound-induced biological effect, the goal of which is to determine the current and future role of diagnostic ultrasound relative to this biological effect. The medical profession benefits if it is shown that diagnostic ultrasound is a significant medical risk to the patient by advising clinicians about this risk, and suggesting how the clinician can monitor the degree of risk. Likewise, the medical profession benefits if it is shown that diagnostic ultrasound is not a significant medical risk to the patient by eliminating this as a clinical concern. In either case, there is clear medical significance. The data necessary to decide this issue are not currently available. The current status regarding ultrasound-induced lung damage in experimental animals supports the view that diagnostic ultrasound equipment poses a risk to human beings. The proposed studies have been designed to address directly these issues by an interdisciplinary group of investigators who have considerable experimental experience with ultrasound-induced lung damage, lung morphology and lung function research studies, and in addition considerable experimental and theoretical experience with ultrasound biophysics and related physics areas. The experimental (animal-based) and theoretical (mechanism-development) research program has four specific aims, viz., (1) to evaluate ultrasound levels at which minimum detectable lung hemorrhage occurs as a function of species and age; (2) to evaluate the physiological ramifications and function, (3) to evaluate the damage mechanism experimentally; and (4) to develop a theory that addresses one general class of damage mechanisms. The experimental design investigates ultrasound-induced lung hemorrhage as a function of both age and species, and the design of the experimental variables all aim at providing a database that can be used to extrapolate the findings to human beings. The theoretical studies provide a mathematical basis for understanding the basic mechanism so that another approach is available for extrapolating to humans.